1. Field of the Invention
This invention relates to a lamp unit for a light radiating type heating device for heating and processing through light radiation in a process such as film formation, diffusion and annealing or the like of a workpiece such as a semiconductor wafer, and, more particularly, the invention relates to a lamp unit for a light radiating type heating device capable of performing a high speed heating and processing in an annealing step for a semiconductor wafer, for example, to form a shallow connection surface.
2. Description of the Related Art
In semiconductor manufacturing, a light radiating type heating device for performing heating and processing with light containing a large amount of infrared rays radiated from filament lamps is used in order to perform processing such as a film formation, a diffusion and an annealing or the like on the semiconductor wafer. Although all these processing steps comprise a heating operation for heating the semiconductor wafer up to a high temperature, application of a light radiation type heating and processing device enables the semiconductor wafer to be rapidly heated and to increase its temperature up to 1000xc2x0 C. or more within tens and several seconds to several ten seconds, for example. In addition when the light radiation is stopped the semiconductor wafer can be cooled rapidly.
FIG. 1 shows a cross-sectional view of one example of a prior art light radiating type heating device. Filament lamps 4 to be described later are arranged in a lamp chamber 1, and a mirror 5 is installed behind the filament lamps 4. A light radiation chamber 2 and a quartz window 9 define this lamp chamber 1. Within the light radiation chamber 2, a semiconductor wafer W as the work piece to be heated and processed is mounted on a wafer holding block 3. In addition, a quartz window 9 is used in the case that the atmosphere near the semiconductor wafer W is different from the atmosphere in the lamp chamber 1.
One example of the filament lamp 4 is illustrated in FIG. 2, wherein a seal member for the filament lamp 4 is comprised of an annular light emitting tube 7 and a pair of inlet tubes 8 cooperatively arranged at a right angle to the end part of the light emitting tube 7, and a filament 12 having a tungsten raw wire wound in a helical form is installed within the light emitting tube 7. A seal section 11 is formed at the end part of each inlet tube 8, and the end part of the filament 12 and the lead wire 19 are connected in the seal section 11 through a molybdenum foil 11a. The sealed member is filled with a small amount of halogen gas together with inert gas. As shown in FIG. 3, the annular light emitting tubes 7 of the filament lamp 4 are constructed such that the light emitting tubes 7 of semi-circular or a circle segment or arcuate shape are combined to form a circular shape.
In FIG. 1, the light emitting tubes 7 are of circular shape, and a plurality of filament lamps 4 having different annular diameters D are arranged such that the light emitting tubes 7 are installed in a concentric manner around a center X of the circle. In FIG. 1, seven filament lamps 4 are used. The mirror 5 arranged behind the filament lamps 4 is made of metal, for example, aluminum, and there are provided some concentric grooves 13 covering the light emitting tubes 7 of the filament lamps 4 and passage holes 6 into which the inlet tubes 8 are inserted. The reflecting surface of the mirror 5 is provided with a metallic plating, for example, gold plating so as to attain a superior reflection of light.
The light emitting tube 7 of each of the filament lamps 4 is arranged and fitted in the concentric grooves of the mirror 5. In addition, the inlet tube 8 of each of the filament lamps 4 is inserted into the passage hole 6 of the mirror 5 and protrudes from the rear surface of the mirror 5, and a lead wire 19 is connected to an electrical circuit.
Accordingly, when electric power is fed to the filament lamps 4, a filament 12 may produce and radiate light. The light is reflected by the mirror 5 and radiated against the semiconductor wafer W within the light radiating chamber 2.
In recent years, it has become necessary to attain a high-integrated formation and ultra fine arrangement of a semiconductor integrated circuit, and it is most important to obtain a thin diffusion layer containing some impurities and to form a shallow junction surface during a stage in which the impurities are, for example, through ion implanting process, implanted into and diffused in the silicon crystal of the semiconductor wafer. The diffusion of impurities through the ion implanting process is carried out at an implanting stage in which the ionized impurities are accelerated by an electric field and physically implanted into the silicon crystal and also at an annealing stage in which the impurities are diffused in the crystal while damages to the crystal through implanting the impurities are repaired. It is necessary to restrict the diffusion of impurities in order to attain a thin diffusion layer in the annealing stage so as to form a shallow junction surface and further to obtain a thin diffusion layer. It is therefore necessary that the temperature increasing speed of the semiconductor wafer is higher than that of the prior art. If the temperature increasing speed is slow the annealing processing time is extended and the diffusion of the impurities exceeds a predetermined diffusion layer thickness which becomes too large. In turn, if the layer thickness of the diffusion layer is required to be in the range of 0.13 to 0.15 xcexcm, for example, it becomes necessary to reach a temperature increasing speed of 150 to 200xc2x0 C./sec.
However, in order to reach a faster temperature increasing speed than that of the prior art it is necessary to increase the lamp input density (the lamp input per unit area). In order to increase the lamp input density in the device shown in FIG. 1, one may think of arranging the lamps in several layers as shown in FIG. 4.
With such an arrangement as above, the projection of the arrangement of the filaments of the lamp on the radiation surface causes the density of the filaments to be increased as compared with that shown in FIG. 1 so that the lamp input density is increased. However, the lamp envelope is highly heated by the energy radiated from the adjoining lamps (either the lamp 7A or 7B in the same plane or lamps 7A and 7B in a different layer).
Although the envelope of the filament lamp 4 is made of quartz glass, the quartz glass absorbs light from the filament 12 and reaches a high temperature. When the temperature reaches 800xc2x0 C. or more the quartz glass recrystallizes, begins to show white turbidness and loses its transparency. When the envelope loses its transparency the light from the filament 12 hardly passes through the envelope resulting in that the desired energy cannot be radiated against the semiconductor wafer W as the workpiece to be processed.
In order to prevent the envelope of the lamp from losing its transparency it is necessary to perform an efficient cooling of each of the lamps. However, as is apparent from FIG. 4, a lamp may be irradiated with light from four adjoining lamps so that a large stream of cooling air must be blown against a lamp so as to decrease the temperature of the envelope of the lamp down to a temperature where the loss of transparency can be prevented. Further, the cooling air has to be uniformly applied to any of the plurality of annular lamps. However, the components used for blowing a large stream of cooling air uniformly against the plurality of annular lamps or for discharging the air or the like are large in size and complicated.
In view of the foregoing, it is an object of the present invention to provide a lamp unit for a light radiating type heating device in which an efficient cooling of the lamps may easily be carried out and the temperature increase of a workpiece such as a semiconductor wafer is faster than in the prior art without making the cooling structure for the lamps complicated and large.
The object of the present invention is attained in a first embodiment by providing a lamp unit for a light radiating type heating device comprising a first group of lamps comprising a plurality of filament lamps, wherein each filament lamp has a light emitting tube arranged in a first plane and wherein said filament lamps are arranged such that their light emitting tubes form concentric circles having different diameters; and a second group of lamps comprising a plurality of filament lamps, wherein each filament lamp has a light emitting tube arranged in a second plane and wherein said filament lamps are arranged such that their light emitting tubes form concentric circles having different diameters, wherein said first plurality of filament lamps and said second plurality of filament lamps are arranged in a staggered manner having coincident centers; said lamp unit further comprising a mirror for reflecting light emitted from said filament lamps, said mirror comprising grooves wherein the light emitting tubes of the filament lamps of the first group of lamps are arranged, and wherein the grooves are defined by side walls protruding from said mirror in the direction of the light emitting tubes of the filament lamps of the second group of lamps.
In addition, in a preferred embodiment, the mirror is provided with at least one hole exclusively used for aeration in order to perform an efficient cooling of the lamps.
As described above, the present invention provides a lamp unit for a light radiating type heating device in which light emitting tubes form an annular shape and a plurality of filament lamps are arranged in the same plane in a concentric manner to constitute a group of lamps such that the light emitting tubes form concentric circles having different annular diameters and a plurality of groups of lamps are arranged in a staggered manner with their centers coincident with each other. Behind the rear surfaces of the light emitting tubes of the filament lamps a mirror is arranged, and the side walls of said mirror protrude between the filament lamps of one group of lamps up to the light emitting tubes of the filament lamps of another group of lamps so that the arrangement pitch of the filament lamps can be made small and the lamp input density can be increased without increasing each lamp input. Accordingly, the temperature increasing speed of the semiconductor wafer can be made fast as compared with that of the prior art and it becomes possible to serve the requirement of making a shallow junction surface at the annealing stage of the semiconductor wafer processing. The adjoining light emitting tubes within the same plane are partitioned by the side wall of the mirror and the adjoining light emitting tubes at the different height level (in different lamp planes) shield part of the radiated light resulting in that it is possible to reduce the degree of heat being absorbed by the adjoining filament lamps. Accordingly, it is not necessary to provide for a large and complicated cooling structure for the filament lamps as in the prior art.
In addition, since the mirror is provided with the exclusive holes for aeration and the entire lamp is air-cooled, it is possible to perform an efficient cooling of the lamps even if the lamp input is high, and further a loss of transparency of the lamp can be prevented.